extract.boot.modmed.mlm {multilevelmediation}

Post-processing of bootstrap results from boot.modmed.mlm

Description

Post-processing of bootstrap results from boot.modmed.mlm

Usage

extract.boot.modmed.mlm(
  boot.obj,
  type = c("indirect", "a", "b", "cprime", "covab", "indirect.diff", "a.diff", "b.diff",
    "cprime.diff"),
  ci.type = "perc",
  ci.conf = 0.95,
  modval1 = NULL,
  modval2 = NULL
)

Arguments

boot.obj

Result of boot using boot.modmed.mlm

type

Character indicating which piece of information to extract from the model "indirect": value of the indirect effect. "a": Current value of a path. "b": Current value of b path. "cprime": Current value of c path. "covab": Random effect covariance between a and b paths, if both paths have associated random effects. "indirect.diff": difference in indirect effect at two values of the moderator (set by modval1 and modval2). "a.diff": difference in a at two values of the moderator (set by modval1 and modval2). "b.diff": difference in b at two values of the moderator (set by modval1 and modval2). "cprime.diff": difference cprime at two values of the moderator (set by modval1 and modval2).

ci.type

Character indicating the type of confidence interval to compute. Currently only percentile confidence intervals are supported with "perc".

ci.conf

Numeric value indicating the confidence level for the interval.

modval1

If enabled, other quantities such as the indirect effect, a, b, and cprime, will be computed at this particular value of the moderator. Otherwise, value of these quantities is directly extracted from the model output (i.e., these would represent values of the effects when the moderator = 0).

modval2

Second value of the moderator at which to compute the indirect effect.

Details

This is a convenience function that computes point estimates and confidence intervals from multilevel mediation analysis models where boot.modmed.mlm was used along with the boot package, or bootresid.modmed.mlm was used. This function generally assumes that type="all" was used when initially fitting the model, making all necessary information available for computation of indirect effects, differences between effects, and so on. If type="all" was not used, there is no guarantee that confidence intervals for the effects of interest can be extracted.

Value

A list with the following elements:

• CI A vector, typically two elements, that has the lower and upper endpoints requested confidence interval for the quantity requested by type.

• est Point estimate for the quantity requested by type.

Examples

## Mediation for 1-1-1 model
library(boot)

data(BPG06dat)

set.seed(1234)

# Note that R should be be MUCH larger than the value used here (e.g., 1000 or
# larger). A small number is chosen just so examples run relatively fast when
# tested.

# bootstrap all fixed and random effects
boot.result<-boot(BPG06dat, statistic=boot.modmed.mlm, R=5,
   L2ID = "id", X = "x", Y = "y", M = "m",
   random.a=TRUE, random.b=TRUE, random.cprime=TRUE,
   type="all",
   control=list(opt="nlm"))

# Point estimate and 95% CI for indirect effect
extract.boot.modmed.mlm(boot.result, type="indirect", ci.conf=.95)